Storage cathode ray tubes



' March 23, 1965 E. B. B. CALLICK ETAL 3,175,114

STORAGE CATHODE RAY TUBES Filed March 51, 1961 INvEN'roRs ATTORNEY-5,

United States Patent 3,175,114 a STORAGE CATHODE RAY TUBES Eric Brian Butler Callick, Chelmsford, and Jervois Campbell Firrniu, Little Baddow, England, assignors to English Electric Valve Company Limited, London, England, a British company 7 Filed Mar. 31, 1961, Ser. No. 99,818 Claims priority, application Great Britain, May 2, 1960, 15,284/ 60 6 Claims. (Cl. 313-67) This invention relates to storage cathode ray tubes and has for its object to provide improved storage tubes.

According to this invention a storage cathode ray tube comprises a foraminous charge storing target structure; an electron gun adapted to provide an electron beam movable across said structure; means, controllable by signals to be stored, for causing said beam to produce on said target structure, as the beam moves across it, a charge pattern representative of said signals whereby said beam is utilisable as a writing beam; and at least one collector electrode positioned to receive beam electrons controlled in amount by the charges on dilferent parts of said target structure and moving away from the target whereby said beam may also be used as a reading beam and, when so used, will divide at said target structure, in dependence on the charges thereon, into two portions one of which passes through said structure to move away therefrom in the same direction and the other of which is repelled by said structure to move away therefrom in the opposite direction, said collector electrode being positioned to receive a portion of the beam electrons moving away from the target structure.

The collector electrode may be positioned on the side of the target structure remote from the gun, in which case it will receive said one portion, or it may be positioned on the gun side of said structure, in which case it will receive said other portion. Theoretically, it is possible to provide two collector electrodes, one in each position, which will receive electron. strengths simultaneously varying in opposite directions and the tube will have two outputs. This, however, is not preferred.

In one convenient embodiment, however, a collector electrode is positioned to receive the aforesaid other portion and a fluorescent screen is positioned to receive the aforesaid one portion and thus produce a visual image.

In accordance with a preferred feature of this invention the collector electrode is made the first electrode of an electron multiplier, the final electrode of which is the output electrode of the tube. This enables the strength of the beam when used for reading to be made quite small and a goodoutput signal still obtained and provides the further advantage of long storage time without deteriora tion of the stored charge pattern.

The signals to be stored may be used to modulate the beam in intensity or they may be employed to deflect the beam in accordance with their variations.

Preferably the foraminous storage target structure includes a storage electrode comprising a conductive grid or mesh having deposited on one side thereof a layer of insulating material and a secondary electron collecting electrode disposed close to but separated from said storage electrode.

In the case in which an electron multiplier is positioned on the gun side of the target structure it is preferably arranged to surround the electron gun.

The invention is illustrated in and further described with reference to the accompanying drawings, of which each of FIGS. 1 and 2 shows one embodiment of the invention. In the drawings like parts are denoted by like references.

Referring to FIG. 1 the storage tube therein shown has an evacuated envelope 1 having an enlarged portion 1a.

At one end of the envelope 1 is an electron gun comprising a cathode 2 and grids 3 and 4, the gun being arranged to produce a narrow, parallel sided electron beam, and an anode 5 is provided in the form of a metallic deposit on the tube wall to accelerate the electrons of the beam.

Within the enlarged portion 1a and transverse to the envelope is a foraminous storage electrode 6 which comprises a metallic grid or mesh backing electrode 6' having deposited thereon, on the side towards the electron gun, a layer of insulating material 6". The insulating layer 6 is so arranged that it does not occupy the interstices of the backing electrode 6'. Closely spaced from the storage electrode 6 and parallel thereto are two grids or meshes 7 and 8, one on each side, the grid 7 on the side nearer the electron gun being adapted to act, in operation, as an electron collecting grid and the grid 8, on the side of the storage electrode 6 remote from the electron gun, being adapted to operate as an accelerating grid. The provision of the accelerating grid 8 is not a necessity, although its use is preferred.

At the opposite end of the tube from the electron gun is an electron multiplier which is conventionally represented as a number of dynodes 9 and an output electrode 10.

In operation the cathode 2 is initially held at a reference potential, for example at earth, and the insulating layer 6". of the storage electrode is stabilised by means of the electron beam at a potential which is slightly negative. This may be achieved as follows. The backing electrode 6' is raised to a potential which is above the so-called first secondary emission crossover potential and which is slightly above the potential of the collector grid 7. In the drawing typical values of potential, which are by way of example and are in no sense limiting, are given. The electron beam, which is focussed by means of an immersing magnetic field provided by the coil 11, is scanned across the storage electrode 6, by means of the deflecting coil system 12. Due to the secondary electrons given off by the insulating layer 6 and collected on the collector grid 7 the layer 6" becomes stabilised at the collector grid potential. The potential of the backing electrode 6 is now rapidly reduced to zero, the means for doing this being conventionally represented by the switch 13, and the insulating layer is consequently reduced to a slightly negativepotential.

The potential of the cathode 2 is now reduced to a value in excess of the first crossover of the layer 6", by means exemplified as a switch 14, and the signal to be stored is applied to the tube in such manner as to produce on the insulating layer 6 a charge image of the signal. This may be done, for example, by modulating the electron beam while it is scanned in a television raster across the storage electrode 6. Alternatively a constant current beam maybe scanned in one direction across the storage electrode while the signal to be stored is used to deflect the beam in a co-ordinate direction. Other methods of controlling the storage of information on the electrode 6 may, of course, be used.

Where the beam strikes the storage electrode 6 second ary electrons will be given oh and collected by the collector grid 7 and these parts of the storageelectrode will increase positively in potential. to an extent determined by the beam current so that a charge pattern corresponding to the applied signal will be set up.

When the stored information is to be read out the cathode potential is returned to earth and a constant current beam is scanned in a raster across the storage electrode. This beam is arranged to be of such velocity in relation to the potential to which the insulating layer 6" was initially set that unwritten parts of the storage electrode will repel all the beam electrons. Where the insulating layer 6" has been driven more positive, however, during the writing operation, some of the beam electrons will pass through the interstices of the storage electrode, the proportion of electrons passing through the storage electrode at any point being dependent on the potential at that point.

The electrons passing through the storage electrode are accelerated by the accelerating mesh 8 and deflected by means of the coil system 15 on to the dynodes 9 of the electron multiplier and output signals corresponding to the stored signals are taken ofl from the output electrode 10.

The reading operation may be repeated continuously a very large number of times without any serious deterioration in the quality of the reproduced signal information.

FIG. 2 shows a modification of the arrangement of FIG. 1 which needs little further description in view of the description already give in relation to FIG. 1. As will be seen, in the arrangement of FIG. 2 the secondary electron multiplier is placed on the other side of the storage electrode 6 and surrounds the electron gun, while a fluorescent screen 16, which is preferably backed by a thin layer of metal in well known manner, is positioned on an end wall of the tube parallel to and closely spaced from the storage electrode 6. There is no accelerating grid 8.

The operation of the tube of FIG. 2 is similar to that of the tube of FIG. 1 and differs from it in that the portion of the beam electrons which is repelled by the storage electrode 6 impinges on the dynodes 9 of the electron multiplier while that portion of the electron beam which passes through the storage electrode strikes the fluorescent screen, to which accelerating potential is applied, and gives a visual indication of the stored information. As will be apparent the deflection coil system 12 serves both to scan the beam across the storage target and to return the repelled portion of the beam to the electron multiplier.

The invention is not limited to the particular embodiments above described. For example a further modification of the arrangement of FIG. 1 may consist of the simple addition of an electron multiplier around the electron gun. Such a tube would then produce two output signals, one of which would be a mirror image of the other. This arrangement is not, however, preferred.

It will be seen that the storage tubes provided by the present invention require the provision of only one beam deflection system for both reading and writing operations, are of high sensitivity due to the employment of an electron multiplier and are capable of long storage as a result of the use of a low energy reading beam.

We claim:

1. A storage cathode ray tube for storing electrical signals comprising an envelope; a foraminous charge storing target structure mounted within said envelope and including a conductive grid or mesh having deposited on one side thereof a layer of insulating material; electron gun means disposed within said envelope for producing a pencil-like electron beam; deflecting means for scanning said beam across said target structure; means, controlled by the signals to be stored, for causing said beam to produce a charge pattern representative of said signals on said target structure during signal storage; a fluorescent screen positioned at the end of said envelope remote from said electron gun means; and at least one collector electrode providing electrical signal output from said tube during readout and being positioned at the gun end of said envelope to receive an amount of beam electrons controlled by the charges on the different parts of said target structure, the beam being divided into two portions at said target structure in accordance with the charges thereon, one portion passing through said target structure and the other portion being repelled by said target structure; said fluorescent screen being positioned to receive said one portion and providing a visual output from said tube; and said collector electrode being positioned to receive said other portion and providing said electrical signal output.

2. A tube as claimed in claim 1, wherein said means for causing said beam to produce a charge pattern on said target structure comprises means responsive to the signals to be stored for modulating the intensity of the electron beam.

3. A tube as claimed in claim 1, wherein said means for causing said beam to produce a charge pattern on said target structure comprises means responsive to the signals to be stored for deflecting the electron beam in accordance with their variations.

4. A tube as claimed in claim 1 and wherein the collector electrode constitutes the first electrode of an electron multiplier, tne final electrode of which is the output electrode of the tube.

5. A tube as claimed in claim 4 wherein the electron multiplier is arranged to surround the electron gun.

6. A storage cathode ray tube for storing electrical input signals comprising an evacuated envelope; a foraminous charge storing target structure mounted transversely within said envelope and including a conductive grid or mesh having deposited on one side thereof a layer of insulating material; writing means for storing said input signals on said target structure, said writing means comprising an electron gun for providing an electron beam, deflecting means for scanning said beam across said target structure, and means controlled by said input signals for causing said beam to produce a charge pattern representative of the input signals on said target structure; and reading means for providing both visual and electrical signal outputs representative of the stored signals, said reading means comprising said electron gun and said deflecting means, a fluorescent screen located at the end of said envelope remote from the electron gun, at least one collector electrode located at the gun end of said envelope, means for positioning the collector electrode with respect to the target structure to receive an amount of beam electrons determined by the stored charge pattern which divides the electron beam into two portions at said target structure, in accordance with the charges thereon, one portion passing through said target structure and the other portion being repelled thereby, and means for positioning said fluorescent screen to receive said one portion and to provide said visual output, said collector electrode receiving said other portion and providing said electrical signal output.

References Cited by the Examiner UNITED STATES PATENTS 2,834,900 5/58 McCarthy 313-68 2,872,612 2/59 DeLano et al. 31368 X 2,873,398 2/59 Crost 31.368 X 2,887,597 5/59 Smith et al. 3l368 2,922,071 1/60 Hergenrother 313-68 X 2,969,477 1/61 Gebel 3l3-68 GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, DAVID J. GALVIN, Examiners. 

1. A STORAGE CATHODE RAY TUBE FOR STORING ELECTRICAL SIGNALS COMPRISING AN ENVELOPE; A FORAMINOUS CHARGE STORONG TARGET STRUCTURE MOUNTED WITHIN SAID ENVELOPE AND INCLUDING A CONDUCTIVE GRID OR MESH HAVING DEPOSITED ON ONE SIDE THEREOF A LAYER OF INSULATING MATERIAL; ELECTRON GUN MEANS DISPOSED WITHIN SAID ENVELOPE FOR PRODUCING A PENCIL-LIKE ELECTRON BEAM, DEFLECTING MEANS FOR SCANNING SAID BEAM ACROSS SAID TARGET STRUCTURE; MEANS, CONTROLLED BY THE SIGNALS TO BE STORED, FOR CAUSING SAID BEAM TO PRODUCE A CHARGE PATTERN REPRESENTATIVE OF SAID SIGNALS ON SAID TARGET STRUCTURE DURING SIGNAL STORAGE; A FLUORESCENT SCREEN POSITIONED AT THE END OF SAID ENVELOPE REMOTE FROM SAID ELECTRON GUN MEANS; AND AT LEAST ONE COLLECTOR ELECTRODE PROVIDING ELECTRICAL SIGNALS OUTPUT FROM SAID TUBE DURING READOUT AND BEING POSITIONED AT THE GUN END OF SAID ENVELOPE TO RECEIVE AN AMOUNT OF BEAM ELECTRONS CONTROLLED BY THE GHARGES ON THE DIFFERENT PARTS OF SAID TARGET STRUCTURE, THE BEAM BEING DIVIDED INTO TWO PORTIONS AT SAID TARGET STRUCTURE IN ACCORDANCE WITH THE CHARGES THEREON, ONE PORTION PASSING THROUGH SAID TARGET STRUCTURE AND THE OTHER PORTION BEING REPELLED BY SAID TARGET STRUCTURE; SAID FLUORESCENT SCREEN BEING POSITIONED TO RECEIVE SAID ONE PORTION AND PROVIDING A VISUAL OUTPUT FROM SAID TUBE; AND SAID COLLECTOR ELECTRODE BEING POSITIONED TO RECEIVE SAID OTHER PORTION AND PROVIDING SAID ELECTRICAL SIGNAL OUTPUT. 